Answer to Question #183576 in Electrical Engineering for John

Question #183576

a) You are required to examine the three main types of communication media (ie twisted pair, coaxial and fibre optic cables) and explain using diagrams the advantages and disadvantages for each type.


b) Select one of the cable from the list and explain how the cable selected can be used for a PLC application.


c) Explain using diagrams, the construction of three types of connectors which are used in PLC communications and select a suitable PLC application for each. 


d) Opto – isolator are used in some PLC devices for communication purposes. Explain using diagrams how the Opto-isolator works and states at least three advantages for using Opto – isolators in PLC applications.

Expert's answer

a. Twisted pair


  • It can be used to carry both analog and digital data.
  • It is relatively easy to implement and terminate.
  • It is the least expensive media of transmission for short distances.
  • If a portion of a twisted pair cable is damaged it does not affect the entire network.


  • It offers poor noise immunity as a result signal distortion is more?
  • Attenuation is very high.
  • It supports lower bandwidth as compared to other Media.
  • It offers very poor security and is relatively easy to tap.
  • Being thin in size, they are likely to break easily.



  • Coax Supports High Bandwidth Levels. When it comes to bandwidth, there seems to be no end to the increasing appetite of consumers.
  • Coax is Easy to Install. Let's face it, coaxial cable is relatively easy to install and fiber can be a real pain.
  • Coax is Easy to Locate.
  • Coax Can Provide Power.
  • Coax is Rugged.


  • One of the major disadvantages of coax is the fact that they are bulky.
  • It is expensive to install for longer distances because of its thickness and stiffness.
  • It needs to be grounded to limit interference.

Fibre optic cables


  • Greater Bandwidth. Copper cables were originally designed for voice transmission and have limited bandwidth.
  • Faster Speeds. Fiber optic cables have a core that carries light to transmit data. ...
  • Longer Distances.
  • Better Reliability.
  • Thinner and Sturdier.
  • More Flexibility for the Future.
  • Lower Total Cost of Ownership.


The optical fibers are difficult to splice, and there is a loss of light in the fiber due to scattering. They have a limited physical arc of cables. If you bend them too much, they will break. The optical fibers are more expensive to install, and they have to be installed by specialists.

b. Fiber-optic communication system has emerged as the most important communication system. Compared to the traditional system because of the following requirements :

  1. In a long-haul transmission system, there is a need for the low loss transmission medium
  2. There is a need for compact and least-weight transmitters and receivers.
  3. There is a need for an increased span of transmission.
  4. There is a need for an increased bit rate-distance product. A fiber optic communication system fulfills these requirements, hence most widely accepted.

c. Board-to-Board Connectors

Board-to-board connectors are used to connect PCBs without a cable. The board-to-board connectors can save space on cables, making them suitable for systems with limited space. The PCBs can be connected using connectors in parallel or perpendicular configuration. A connector that connects two PCBs in a stacking configuration is called a mezzanine connector. However, the term is sometimes used to describe perpendicular or side-by-side PCB arrangements. These arrangements are usually seen for motherboard–daughterboard arrangements, where the focus is on the parallel arrangement.

Wire/Cable-to-Wire/Cable Connectors

wire-to-wire connectors connect two wires, as the name suggests. One end of the connector is permanently connected to the wire. The other end of the connector forms a separable interface. The permanent connection can be made using either crimping or insulation displacement contact (IDC). In the IDC method, the connection is made by inserting the insulated wire into a slot of a sharpened metal beam. The sharp edges of the beam cut through the insulation and make a rigid metal-metal contact between the wire and the beam.

Wire/Cable-to-Board Connectors

A wire-to-board connector, as the name suggests, connects a wire/cable to a PCB. The wire connections are similar to the one used for wire-to-wire connection, and the board connections are, for the most part, press-in or soldered two-piece connectors; although, some card edge versions remain in use. The mating interface for the separable connection may be identical to that of a wire-to-wire connector from the same product family. While there are many applications of wire-to-board connectors, the trend is toward cable-to-board connectors, or cable assemblies, to take advantage of the benefits of IDC.

d. An optoisolator is a device that consists of a light-producing device such as LED and a light-sensing element such as a phototransistor. When a voltage is applied to the LED, light is produced which strikes the photodetector. The photodetector then changes its output. Optoisolator provides electrical isolation between the input and output sides. Optoisolator is an important part of the I/O module of PLC. Both input and output modules have Optoisolator to achieve electrical isolation between the outside electrical circuit and the PLC circuit.

An optoisolator is a semiconductor device that uses a short optical transmission path to transfer an electrical signal between circuits or elements of a circuit while keeping them electrically isolated from each other. Optocouplers can be used to isolate low-power circuits from higher power circuits and to remove electrical noise from signals. Electronic equipment, as well as signal and power transmission lines, are subject to voltage surges from radio frequency transmissions, lightning strikes, and spikes in the power supply. To avoid disruptions, optoisolators offer a safe interface between high-voltage components and low-voltage devices.

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